1. Field of the Disclosure
The present disclosure relates to directional drilling and, in particular, to a method of determining a location of a well drilled with respect to a pre-existing reference well.
2. Description of the Related Art
Passive magnetic ranging arises out of the need to accurately determine the location of an existing well relative to a well being drilled. Relative position accuracy from survey-derived estimates is often insufficient due to the accumulation of measurement errors as the depth of the well increases. Passive magnetic ranging is a process for determining a relative position of a magnetic source in a reference well with respect to a magnetometer in a new well. A number of measurements and variables are used to determine the relative position. Exemplary measurements include, but are not limited to, measurement of the earth's magnetic field, orientation of the sensor, the strength and distribution of the source field (i.e., the residual magnetic fields in the reference well), sensor biases, scale factors, etc. These variables and measurements have uncertainties associated with them that make it difficult to determine relative position from a single magnetometer vector measurement. Thus, there is a need for improved methods for directional drilling of a well next to a reference well that account for all such error sources.